What are some online courses on artificial general intelligence?
There are at least three free courses.

MIT 6.S099: Artificial General Intelligence, organized by Lex Fridman, is a series of lessons and talks primarily given by a diverse set of guest appearances, such as

Josh Tenenbaum (researcher and professor in computational cognitive science),
Nate Derbinsky (who gives a lesson on cognitive architectures, Soar, etc.),
Stephen Wolfram (creator of Mathematica, Wolfram Alpha and the Wolfram Language; he talks about his work throughout the years, especially, the development of Wolfram Alpha and Language),
Marc Raibert (CEO of Boston Dynamics, who gives a lesson on his work at Boston Dynamics and the robots they have developed),
Lisa Feldman Barrett (professor of psychology, who gives a very insightful lesson on emotions and feelings, with possibly different perspectives),
Rosalind Picard (a professor at MIT, director of the Affective Computing Research Group at the MIT Media Lab, and co-founder of two companies, Affectiva and Empatica; in her talk with Lex, she talks about affective computing and other interesting concepts and issues)
Marcus Hutter (inventor of a mathematical theory of general intelligence, AIXI; in his talk with Lex, he talks about Occam's razor, Solomonoff induction, Kolmogorov complexity, the definition of intelligence, AIXI, rewards, bounded rationality and consciousness)


Knowledge-Based AI: Cognitive Systems (taught by Ashok Goel and David Joyner)

The Society of Mind (taught by Marvin Minsky, who also wrote a book and developed a theory of natural intelligence with the same name)

CS 294-149: Safety and Control for Artificial General Intelligence (Fall 2018) (see also these notes)